Usually they wait till there is some red blush.
I do pretty good at staying ahead of the birds and squirrels. I've been picking loads of cherry tomatoes, started picking Merceds and a hugely proflific mystery tomato which simply volunteered itself.
Last Spring I learned you can't trust your eyes. Squirrels can smell when a tomato is good enough to eat. For the first time, I planted two Aunt Ruby German Green tomato plants which produced a fair number of large tomatoes. The squirrels ate half of each tomato on the vine. I couldn't tell when the fruit ripened. But the squirrels could! They passed over the reds in favor of the greens!
Planted two more this Spring. They've produced fruit and you can bet I'm checking them every day for the slightest color change. Don't want to share them with no darn squirrels.
It was really strange. Usually I would find green tomatoes on the ground with just one bite missing. These 2 were just totally gone, like they picked them and ate or buried the whole thing.
The rest of the tomatoes are way behind with one ore two marble size, and the rest just flowers. We set some traps to catch them so we can haul them off, but we have lots of nut trees, so every spring we have a bunch of new ones.
We also have lots of wild rabbits along the back fence which is adjacent to about 3 acres of undeveloped land filled with trees and brambles.
In a way it’s good. If food prices get too high to buy chicken etc. we can always fry up a squirrel or rabbit. LOL.